CMPE 80N - Introduction to Networks and the Internet 1 CMPE 80N Winter 2004 Lecture 18 Introduction to Networks and the Internet

CMPE 80N - Introduction to Networks and the Internet 2 Announcements Fourth quiz on Monday, March 1 st. Third HTML discussion session today by Kiran (before class). Summary posted on the Web page. FINAL HTML discussion session by Debasree on Thu 3-4pm in BE 109. Quiz review session on Friday by Kiran in BE 354I from 4:45-5:45. –Practice quiz. In order to schedule a second review session, we will wait to hear from you first.

CMPE 80N - Introduction to Networks and the Internet 3 Networks and IP addressing IP address: –Network part + Host part Network: –Any host can physically be reached by any other host without intervening router –All hosts in the same network have the same network number network consisting of 3 IP networks (for IP addresses starting with 223 (class C), first 24 bits are network address).

CMPE 80N - Introduction to Networks and the Internet 4 Routing Table (revisited) A B E Dest. Net. next router Nhops routing table in A

CMPE 80N - Introduction to Networks and the Internet A B E Datagram from A to B: look up net. address of B find B is on same net. as A link layer will send datagram directly to B inside link-layer frame B and A are directly connected Dest. Net. next router Nhops misc fields data Routing Example 1

CMPE 80N - Introduction to Networks and the Internet A B E Dest. Net. next router Nhops Datagram from A to E: look up network address of E E on different network A, E not directly attached routing table: next hop router to E is link layer sends datagram to router inside link-layer frame datagram arrives at continued….. misc fields data Routing Example 2

CMPE 80N - Introduction to Networks and the Internet A B E Arriving at , destined for look up network address of E E on same network as router’s interface router, E directly attached link layer sends datagram to inside link-layer frame via interface datagram arrives at !!! (hooray!) misc fields data network router Nhops interface Dest. next Routing Example 2 (cont’d)

CMPE 80N - Introduction to Networks and the Internet 8 The Internetworking Layer The Internet as a collection on networks or autonomous systems (ASs). Hierarchical structure. US backbone European backbone Regional network National network Transcontinental links Transcontinental links

CMPE 80N - Introduction to Networks and the Internet 9 The Internet Protocol: IP Glues Internet together. Common network-layer protocol spoken by all Internet participating networks. Best effort datagram service: –No reliability guarantees. –No ordering guarantees.

CMPE 80N - Introduction to Networks and the Internet 10 IP (cont’d) IP is responsible for datagram routing. Important: each datagram is routed independently! –Two different datagrams from same source to same destination can take different routes! –Why? –Implications?

CMPE 80N - Introduction to Networks and the Internet 11 IP (cont’d) IP provides a best effort delivery mechanism –Does not guarantee to prevent duplicate datagrams, delayed and out-of-order delivery, corruption of data or datagram loss Reliable delivery is provided by the transport layer, not the network layer (IP) Network layer (IP) can detect and report errors without actually fixing them

CMPE 80N - Introduction to Networks and the Internet 12 Datagrams Transport layer breaks data streams into datagrams which are transmitted over Internet, possibly being fragmented. When all datagram fragments arrive at destination, reassembled by network layer and delivered to transport layer at destination host.

CMPE 80N - Introduction to Networks and the Internet 13 IP Datagram Format IP datagram consists of header and data (or payload). Header: –20-byte fixed (mandatory) part. –Variable length optional part.

CMPE 80N - Introduction to Networks and the Internet 14 IP Versions IPv4: IP version 4. –Current, predominant version. –32-bit long addresses. IPv6: IP version 6. –Evolution of IPv4. –Longer addresses (16-byte long).

CMPE 80N - Introduction to Networks and the Internet 15 IP(v4) Header Format Header Payload

CMPE 80N - Introduction to Networks and the Internet 16